PROJECT SUMMARY The overall goal of this study is to understand how health information exchange can be leveraged to improve outcomes for Medicaid patients with mental illness. Mental health-related ED visits have increased by more than 50% in the past decade, with Medicaid absorbing the majority of the associated acute-care costs. Medicaid patients with mental illness often experience fragmented care and poor outcomes, including high rates of preventable ED visits and hospitalizations, compared to those without mental illness. Consequently, reducing preventable hospital use has been a central goal of state Medicaid agencies. Patients with frequent use of emergency services are key target group for interventions to improve care delivery, yet their clinical needs are profoundly different from other patients - over half have a mental health or substance use disorder, more than a third have multiple chronic conditions, and 65% are disabled. Health information exchange (HIE) is a promising strategy to facilitate care coordination for these high-needs Medicaid patients. In 2012, Washington state mandated all hospitals to implement and strategically use an HIE referred to as the Emergency Department Information Exchange (EDIE) as part of its ?ER is for Emergencies? program. EDIE was designed to assist hospitals with identifying frequent users of emergency services, facilitate the active development care plans and case management for high-needs patients, and improve data sharing between outpatient providers and hospitals. The use of EDIE, especially the development of electronic care plans, is supported by a variety of policy levers and financial incentives to hospitals, as well as a public-private partnership that makes recommendations for ongoing improvement at the state-level. Yet, to date, its impact on patient outcomes has not been systematically evaluated. Despite this, EDIE and similar HIE platforms are currently being rolled-out in several other state Medicaid programs. Thus, the proposed study aims to understand whether and how EDIE has improved mental health outcomes for frequent users of the ED in Washington state. Using longitudinal Medicaid claims linked to a variety of administrative data sources on hospital and community characteristics we will 1) examine trends in the uptake of EDIE across hospitals, 2) determine the extent to which EDIE improved mental health outcomes for patients overall as well as key subgroups of patients with mental illness, and 3) determine the extent to which health system characteristics enhance the effectiveness of EDIE. The proposed work will contribute to our understanding of the effectiveness of HIE-facilitated care coordination, including the populations, hospitals, and communities that are most likely to reap benefits.